These are my personal reasons. I stress personal because everyone is different.

• it doesn’t do what I tell it to do, but what Microsoft thinks I should want
• difficult to automate (I’ve been told this has been getting better, but I’m still not convinced)
• if things don’t work as I expect, I can’t look at the source code

In most cases I’m much less frustrated by using non-Windows alternatives in infrastructure. For example when I build Windows binaries, I use wine on linux.

Btcpayserver. Credit cards etc just forget about self hosting, I worked for a credit card processor in the past, you won’t be able to get through the PCI audit.